(1) Field of the Invention
The present invention relates to a programmable read-only memory (ROM) device and more particularly to a memory device in which information is written into a selected memory cell by applying a high voltage (PV.sub.ce), for controlling the write-in condition, to a terminal (for example, a chip-enable terminal). This enables the memory device to assume a write-in condition. By supplying a write-in current to the bit line connected to the selected memory cell, leakage of the write-in current into adjacent memory cells is prevented.
(2) Description of the Prior Art
Generally, in a programmable ROM device (hereinafter referred to as a PROM device) having junction-shorting-type memory cells or fuse-blown-type memory cells, information is written into a memory cell by applying a high voltage (PV.sub.ce), for controlling the write-in condition, to a terminal (for example, a CE terminal) so that the memory device assumes a write-in condition by applying a write-in current to a bit line and by rendering the potential of a work line to be low, thereby destroying the PN junction of the memory cell or blowing the fuse thereof. In this case, in a PROM device having, for example, junction-shorting-type memory cells, if the junction of a memory cell adjacent to a memory cell into which information is to be written is already shorted, a write-in current sometimes leaks from a bit line through the adjacent memory cell into a word line, thereby disabling the write-in operation in a selected memory cell. This phenomenon occurs when the resistance of the semiconductor substrate on which the memory device is formed is not small enough and causes write-in error in a PROM device. Therefore, it is necessary to avoid the occurrence of such a phenomenon.
In order to prevent the leakage of a write-in current into adjacent memory cells, a conventional PROM device uses a high voltage, for controlling the write-in condition, as an output power supply voltage of each of the decoder driver circuits connected to the word lines, thereby pulling up the potential of all the non-selected word lines to a high voltage, for example, 20 V, which is higher than the potential rise of a bit line caused by applying a write-in current thereto.
However, in the above-mentioned conventional PROM device, since the collector current, and, therefore the base current, of the output transistor of each decoder driver circuit connected to each word line becomes large, it is necessary to use large-sized output transistors, with the result that it is difficult to increase the degree of integration of the PROM device. Moreover, in the above-mentioned conventional PROM device, since the base current of each of the output transistors is large, it is necessary to use, in the pre-stage, large-sized transistors, with the result that the degree of integration of the memory device is decreased and the operating speed thereof is low.